CNC milled PC board

One of my goals for the CNC mill has been to help fabricate PC boards, primarily in terms of cutting out the overall shape and drilling any through holes. For simple boards, however, it is possible to machine the circuit traces into the copper and avoid the entire photo-etching process altogether. I recently had a chance to try this process out, and the results were quite good.

This particular board needed to be circular, and needed to have a rectangular opening for a switch, so CNC routing the outline is really the way to go. The circuit is relatively simple, so it also lends itself well to routing the traces. If I were to etch this circuit the usual way with photoresist, developer, etchant, etc. etc. it would have taken three times as long.

PC board layout in Cadsoft's Eagle


The board was designed in Eagle as usual, but I then used an add-on to Eagle called PCB-gcode to generate gcode from the traces. There are a number of settings to specify depths, tool settings, speeds, etc. but it is fairly self-explanatory.

PCB-GCODE screenshot

I chose some pretty basic settings, which resulted in the following preview:

PC board layout in PCB-GCODE

I was never able to figure out how to generate the outlines using PCB-gcode, so I re-drew them in Mastercam and went from there. PCB-gcode is supposed to have that ability but there appear to be some bugs in the software that limit its ability to deal with circles and arcs. If anyone has made better progress than me I’d love to hear about it.

CNC machining a PCB on G0704 CNC mill Anyway the final product came out pretty good. I was pretty pleased with myself having tightened up the backlash to only .004″ per axis, but after machining .024″ wide traces I realized how bad that is. Under the right circumstances this is a good technique to save time, but I wouldn’t try to machine extremely fine traces or tight-pitched pads until I work those last few thousandths of backlash out of my machine.






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